There is considerable evidence for regulation of steroid synthesis at the enzyme level, but most of the reported data has been obtained from crude or partially purified systems. Before a unified theory of adrenal control can be established in the complex environment of the intact cell, it is necessary to determine how these overall changes in enzyme activity occur. It is our aim to study the metabolic effect of ACTH and other activators of steroidogenesis on the intact adrenal cell, determine possible regulatory enzyme sites, and develop methods for the isolation of these enzymes as purified proteins. The availability of these purified enzymes should permit a study at the molecular level of the possible mechanisms for controlling the levels of enzyme activity in the intact cell. ACTH-responsive steroidogenic adrenal tumor cell lines which can be maintained in monolayer tissue culture provide a useful model system for such studies. Specific areas of investigation will include: 1. The role of cyclic-AMP in the stimulation of steroidogenesis by ACTH and a search for mutant cell lines lacking ACTH or cyclic-AMP receptor proteins, cyclic-AMP responsive kinases, etc. 2. Continued studies of the relationship of the energy metabolism of the cell to steroidogenesis and 3. an analysis of the mechanism by which the action of ACTH is reversed upon its removal.